Microstructured arrays for cortex interaction and related methods of manufacture and use

ABSTRACT

A brain implant system consistent with embodiments of the present invention includes an electrode array having a plurality of electrodes for sensing neuron signals. A method for manufacturing the electrode array includes machining a piece of an electrically conductive substance to create a plurality of electrodes extending from a base member. Each electrode also has a corresponding base section. A nonconductive layer is provided around at least a portion of the base section of each electrode to support the plurality of electrodes. The base section of the electrodes are then cut to separate the base member from the plurality of electrodes supported by the nonconductive support layer. The present invention also includes a complete brain implant system using the above electrode array.

GOVERNMENT SUPPORT

The U.S. Government has certain rights in this invention as provided forby the terms of grant No. NS25074 and contract No. NO1-NS-9-2322 fromN.I.N.D.S.

BACKGROUND OF THE INVENTION

Recent advances in neurophysiology have allowed researchers to study theactivity of groups of neurons with high temporal resolution and inspecific locations in the brain. These advances create the possibilityfor brain-machine interfaces allowing an amputee to control a prostheticlimb in much the same way that person would control a natural limb.Although noninvasive sensors, such as multichannel electroencephalogram(EEG), have shown some promise as simple interfaces to computers, theydo not currently offer the spatial resolution needed for prostheticcontrol. Current research into the electrical activity of small groupsof neurons has thus been done primarily with arrays of microelectrodesinserted into the brain.

Current intra-cortical microelectrode recording systems can recordelectrical signals from groups of neurons. These systems typically use amicroscopic tapered conductive element, insulated except at its tip, torecord the neuron signals. Other conductor designs, such as blunt cutwires, may record single neurons, but have sub-optimal recordingcharacteristics. Further, nearly all recording systems rely on arrays offixed electrodes connected to data acquisition systems through longwiring or cable harnesses. The percutaneous connectors associated withthese cables present a potential source of infection that limits theuseful life of these systems. The cables themselves also presentadditional problems in the design of a prosthesis that must continue tofunction over many years and not interfere with the patient's dailylife. For instance, the cables limit the patient's mobility by beingtethered to a signal processing device. Relatively long cables may alsopresent a source of electrical interference and may break afterrepetitive use.

The current microelectrode systems for recording single neurons can begrouped into two broad classes: those having microdrive mechanisms andthose having fixed electrode arrays. Systems with microdrive mechanismsallow one to vertically position the electrodes in the brain tissue.Thus, a user can actively search for neurons of interest and accuratelyposition the electrode tip near the soma of the neuron to improve thesignal-to-noise ratio. These systems, however, have their disadvantages.First, even individual microdrive systems are bulky and cannot be fullyimplanted in a human. Second, microdrive systems typically cannot usemore than a few dozen electrodes due to space limitations and the timeit takes to independently position each electrode near a neuron.

Fixed electrode array systems overcome some of these problems, but havetheir own problems as well. Once placed in the brain, fixed electrodearrays can not be repositioned, so they rely on chance proximity toneurons. The most basic fixed electrode arrays record neural activityusing multiple micro-wires or hatpin-like electrodes individuallyinserted into the brain. Because it can take a relatively significantamount of time to insert each electrode, however, these systems have notbeen widely used. More recently, wire bundles have been developed whichare inserted into the cortex as a unit, but they lack features of idealrecording electrodes, such as tip shape, overall size, and impedance. Inparticular, the common square tip of such microwires can damage thecortex and can have difficulty penetrating the tough cerebral membranes,as well as brain tissue.

A major disadvantage of these fixed array systems is that they do notoffer the ability to actively hunt for neurons since the electrode tipscannot be easily placed near the soma of the neurons. To help overcomethis, large numbers of electrodes are inserted to increase the chancethat the electrodes are positioned in close proximity to neurons. Theinput impedances of the electrodes may also be lowered to enhance theirability to record distant signals. Lowering the input impedance,however, also lowers the signal-to-noise ratio.

Accordingly, there is a need for a fixed microelectrode array systemthat may have numerous electrodes providing a high signal-to-noiseratio. Further, there is a need for a fixed array system that has aflexible design and that does not rely upon percutaneous cabling systemsto communicate with a data acquisition system.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a method of manufacturingan electrode array system is disclosed. The method includes machining awork piece of an electrically conductive substance to create a pluralityof electrodes extending from a base member. Each electrode has acorresponding base section. A nonconductive layer is provided around atleast a portion of the base sections of the plurality of electrodes. Thebase member is removed from the plurality of electrodes, such that theplurality of electrodes are supported by the nonconductive layer.

Another aspect of the invention discloses an electrode array. The arrayincludes a flexible nonconductive support layer and an array ofelectrodes. Each electrode has a base section and a tip section, wherethe base section of each electrode is inserted into the nonconductivelayer, such that the electrodes are held together by the nonconductivelayer. An electrical connection located on the base section of eachelectrode communicates with the respective electrode.

In yet another aspect of the invention, a brain implant system comprisesan electrode configured to be inserted in a brain and for sensingelectrical signals generated by brain neurons. A flexible wiring circuitis connected to the electrode and adapted to receive the neuronelectrical signals sensed by the electrode. A processing unit receivesthe neuron electrical signals from the flexible wiring circuit. Theprocessing unit further includes a detection module for detecting theoccurrence of a neuron spike in the received neuron electrical signals.The processing unit also includes a transmitter for transmitting datareflecting the occurrence of each detected neuron spike.

In still another aspect of the invention, a method for operating a brainimplant system, comprises: providing an electrode configured to beinserted in a brain and for sensing electrical signals generated bybrain neurons; receiving the neuron electrical signals sensed by theelectrode over a flexible wiring; receiving the neuron electricalsignals from the flexible wiring and detecting the occurrence of aneuron spike in the received neuron electrical signals; and transmittingdata reflecting the occurrence of each detected neuron spike.

Both the foregoing general description and the following detaileddescription are exemplary and are intended to provide furtherexplanation of the embodiments of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments of thepresent invention, and, together with the description, serve to explainthe principles of the invention. In the drawings:

FIG. 1 is a diagram illustrating an exemplary brain implant systemconsistent with an embodiment of the present invention;

FIG. 2A is a block diagram of a neuron signal processing systemconsistent with an embodiment of the present invention;

FIG. 2B is a block diagram of a power supply system consistent with anembodiment of the present invention;

FIGS. 3A to 3D illustrate exemplary process for making an electrodearray consistent with an embodiment of the present invention;

FIGS. 4A to 4G illustrate an alternative, exemplary process for makingan electrode array consistent with an embodiment of the presentinvention;

FIGS. 5A and 5B illustrate an exemplary wiring, consistent with anembodiment of the present invention, for attachment to an electrodearray; and

FIG. 6 illustrates an exemplary method, consistent with an embodiment ofthe present invention, for connecting an electrode to a wiring.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 generally illustrates a brain implant system consistent with anembodiment of the present invention. As shown in FIG. 1, the systemincludes an electrode array 110 inserted into a patient's cerebralcortex 120 through an opening in the skull 122. Array 110 may include aplurality of electrodes 112 for detecting electrical brain signals orimpulses. While FIG. 1 shows array 110 inserted into cerebral cortex120, array 110 may be placed in any location of a patient's brainallowing for array 110 to detect electrical brain signals or impulses.

Each electrode 112 may be connected to a processing unit 114 via wiring116. Processing unit 114 may be secured to skull 122 by, for example,the use of an adhesive or screws, and may even be placed inside theskull if desired. A protective plate 130 may then be secured to skull122 underneath the surface of the patient's skin 124. In one embodiment,plate 130 may be made of titanium and screwed to skull 120 using screws132. However, the invention may use any of a number of known protectiveplates, such as a biological material, and methods for attaching thesame to a patient's skull. Further, processing unit 114 and othersurgically implanted components may be placed within a hermeticallysealed housing to protect the components from biological materials.

Electrode array 110 serves as the sensor for the brain implant system.While the various figures in this specification illustrate electrodearray 110 as having sixty-four electrodes 112 arranged in an 8×8 matrix,array 110 may include one or more electrodes having a variety of sizes,lengths, shapes, forms, and arrangements. Each electrode 112 extendsinto brain 120 to detect the electrical neural signals generated fromthe neurons located in proximity to the electrode's placement within thebrain. Neurons may generate such signals when, for example, the braininstructs a particular limb to move in a particular way. Electrode array110 is described in more detail with respect to FIGS. 3A to 3D and FIGS.4A to 4G.

Electrodes 112 transfer the detected neural signals to processing unit114 over wiring 116. As shown in FIG. 1, wiring 116 may pass out of theopening in skull 122 beneath protective plate 130. Wiring 116 may thenrun underneath the patient's skin 124 to connect to processing unit 114.Persons skilled in the art, however, will appreciate that arrangementsother than the one shown in FIG. 1 may be used to connect array 110 toprocessing unit 114 via wiring 116. Wiring 116 is described in moredetail below with respect to FIGS. 5A and 5B.

Processing unit 114 may preprocess the received neural signals (e.g.,impedance matching, noise filtering, or amplifying), digitize them, andfurther process the neural signals to extract neural information that itmay then transmit to an external computing device (not shown). Forexample, the external device may decode the received neural informationinto motor control signals for controlling a motorized prosthetic deviceor analyze the neural information for a variety of other purposes.Processing unit 114 is described in further detail with respect to FIG.2A.

FIG. 2A is a block diagram of a processing unit 114 consistent with anembodiment of the present invention. As shown in FIG. 2A, processingunit 114 may further include an analog-to-digital (A/D) interface 210, adetection module 220, a buffer 230, a controller 240, and a transceiver250. In an exemplary embodiment, interface 210, module 220, and buffer230 each may be implemented by a common field programmable gate array(FPGA), although other embodiments are possible. For instance,alternative embodiments may include dedicated hardware or softwarecomponents for implementing subcomponents 210, 220, or 230, such as byusing a microprocessor.

A/D interface 210 may include a plurality of A/D converters, each ofwhich may receive the analog output from a corresponding electrode 112or group of electrodes 112. Each A/D converter may amplify, digitize,and multiplex the signals received from the corresponding electrode(s)112. In one exemplary embodiment, an amplification stage of A/Dinterface 210 may be implemented using a CMOS-based two-stageoperational amplifier known to those skilled in the art, and selected tohave a bandwidth of approximately 300-10 kHz and a gain of about 5000.However, processing units consistent with the present invention may alsoprocess other electrical neural signals, such as those in the 0-100 Hzrange, for example.

For the exemplary embodiment of array 110 comprising an 8×8 matrix ofelectrodes, A/D interface 210 may include eight 12-bit, 37.5 kHz A/Dconverters, each of which receives the analog outputs from eightcorresponding electrodes. In such a case, each A/D converter maymultiplex the electrode channel signals received from a correspondingrow or column of array 110. A/D interface 210 may, however, multiplexother groupings of the electrode channels using any number of A/Dconverters. For instance, A/D interface 210 may include one A/Dconverter that receives the analog outputs from all of the electrodechannels to multiplex those signals into one signal. Alternatively, A/Dinterface 210 may simply convert the electrode channels into digitalsignals without multiplexing. In either case, interface 210 may thenprovide the digital signals to detection module 220.

Detection module 220 detects when a neuron has fired. The signal from asingle neuron essentially comprises a series of electrical spikes. Thebrain encodes information according to the frequency or firing rate ofthese spikes, which is typically between 0 to 300 Hz. The spike itselfmay last about 1.5 ms and may have a peak-to-peak voltage of about 100μV. In systems consistent with an embodiment of this invention,detection module 220 may detect the time a spike occurs since the neuralinformation content is encoded in the timing between the spikes.Alternatively, module may detect the spike count over a predeterminedtime period or may detect instantaneous neural frequencies. In eitherevent, by removing the inter-spike data and reducing the waveform to atime spike representation, module 220 may optimize the wirelesscommunication bandwidth and minimize the storage requirements of thebrain implant system. Buffer 230 may, however, also record informationsufficient to determine the shape of the spike. The ability to determinethe spike's shape may be needed in certain applications, such as whensorting which spikes come from which neurons.

To detect a spike, detection module 220 may detect whether the channelsignal from A/D interface 210 meets a triggering event. Spike detectionmay be based on time, amplitude, or other aspects of the shape of thewaveform. For example, module 220 may detect when the rising edge of aneural signal detected with a particular electrode 112 exceeds apredetermined threshold value in amplitude or time, or a combination ofthe two. Since the spike amplitude may vary among neurons, module 220may vary the threshold value for each electrode 112 based on theparticular neuron(s) being detected by that electrode. In an exemplaryembodiment, detection module 220 may include a programmable 12-bitthreshold for setting the threshold level(s).

Buffer 230 may be implemented by using a pre-trigger and a post-triggerbuffer memory. For instance, a small ring buffer may temporarilypre-store the digital data of a channel prior to a triggering eventdetected by detection module 220. The pre-trigger buffer memory may thusstore those samples corresponding to the spike's shape or other features(e.g., spike slope), prior to the triggering event. Buffer 230 may alsoinclude a separate pre-trigger buffer for each channel or electrode 112,which may store the samples from each channel, according to an exemplaryembodiment. Channel data obtained after the triggering event may then bestored directly in the post-trigger buffer memory to record the timeeach spike occurs and/or the spike shape. In one exemplary embodiment,buffer 230 stores 1.65 ms of recorded data per spike.

Upon triggering, buffer 230 may then output the data of both thepre-trigger and post-trigger buffer memories to transceiver 250. Ifbuffer 230 outputs neural information faster than transceiver 250 maytransmit that information, then buffer 230 may temporarily store theoutputted data in a transmit buffer (not shown). Further, transceiver250 may also transmit only the time of the triggered event of eachdetected neuron signal to increase the transmission rate.

Controller 240 may act as an interface between transceiver 250 and A/Dinterface 210, detection module 220, and buffer 230. Controller 240 mayalso perform certain other control functions, such as setting thetrigger threshold level of module 220 or setting the size of pre-triggeror post-trigger buffers of buffer 230. In addition, controller 240 maybe used to select particular electrode channels for processing andoutputting by transmitter 250. Controller 240 may also manage the powerresources of the electrode array system 100. To each of these ends,controller 240 may include an I/O interface allowing a user to programcontroller 240 to perform the above or other control functions. A usermay thus program controller 240 by transmitting control signals from anexternal control device (not shown) to transceiver 250, which may thenforward the control information to controller 240.

Transceiver 250 provides a wireless communication link betweenprocessing unit 114 and an external device (not shown). In particular,transceiver 250 receives the pre-trigger and post-trigger data stored inbuffer 230 for transmission to the external device for furtherprocessing and storage. Transceiver 250 may transmit the data using“Bluetooth” technology or according to any other type of wirelesscommunication standard, including, for example, code division multipleaccess (CDMA), wireless application protocol (WAP), or infraredtelemetry. Transceiver 250 may also receive control information usingeither of the above communication techniques.

Processing unit 114 may also include a power supply (not shown in FIG.2A) for the brain implant system. FIG. 2B is a block diagram of anexemplary power supply system consistent with an embodiment of thepresent invention. While the power supply system of FIG. 2B allows theimplanted power supply to be recharged, other power supply systems maybe used (such as a typical battery source) that need to be replaced whentheir power is exhausted. As shown in FIG. 2B, a power supply systemconsistent with the invention may include a power supply 260, anamplifier 262, an outside coil or inductor 264, an inside coil orinductor 266, a rectifier circuit 268, a battery recharging circuit 270,and a battery 272. Components 260, 262, and 264 are located outside ofthe patient's body (i.e., outside skin 124) and components 266, 268,270, and 272 are located inside the patient's body.

While each of the components of the power supply system of FIG. 2B areindividually known to those skilled in the art, the particular hardwarechosen to implement components 266, 268, 270, and 272 may beadvantageously chosen based on size, heat requirements, andbiocompatibility. For instance, a preferred embodiment would implementcomponents 266, 268, 270, and 272 by using hardware having a small size,low heat dissipation, and a high biocompatibility with the naturaltissue inside the patient.

Power supply 260 may be any AC power supply, such as a standard 120 voltAC power source. Amplifier 262 receives an AC voltage signal from supply260, amplifies it, and applies the amplified AC voltage signal toinductor 264. When inductor 264 is activated and placed in closeproximity to inductor 266, inductor 264 will induce a current ininductor 266. The induced current then creates an AC voltage on theoutput terminals of inductor 266, which is then applied to rectifiercircuit 268. Rectifier 268 then converts the induced AC voltage signalto a DC voltage signal in a manner known to those skilled in the art.FIG. 2B further shows an optional capacitor 269 for filtering therectified voltage signal. In particular, capacitor 269 may further limitany AC voltage signal levels that may still be present on the rectifiedoutput signal and thereby present a cleaner DC voltage signal. Batteryrecharging circuit 270 then receives the DC voltage signal for chargingbattery 272 located inside the patient. In an exemplary embodiment,battery 272 is a lithium-polymer 3.6 V battery.

FIGS. 3A to 3G illustrate exemplary manufacturing processing steps forpreparing an electrode array consistent with an embodiment of thepresent invention. In particular, FIG. 3A shows a work piece or block ofelectrically conductive material 310 including a plurality of electrodes112. While an exemplary embodiment includes using titanium as material310, a number of other conductive materials may be used, including, forexample, stainless steel, steel, titanium nitride, atitanium-aluminum-vanadium alloy, tungsten carbide, copper, or dopedsilicon. Electrodes 112 may be formed from material 310 by applying awire electrical discharge machining (wire EDM) technique known to thoseskilled in the art. In particular, wire EDM may be used to preciselymachine a raw block of electrically conductive material 310 to formelectrodes 112. Array 110 may be formed by performing a wire EDM cutthrough one plane, rotating array 110 ninety degrees, and thenperforming a second wire EDM cut through a second plane. Other knownmanufacturing methods may, however, be used to micro-machine conductivematerial 310, such as by using a laser or a diamond saw.

Further, a chemical etching process may also be applied to furthermachine electrodes 112. For instance, the machined array of FIG. 3A maybe placed in an etching bath to further etch the electrode surfaces.When material 310 is titanium, for example, a heated hydrochloric orhydrofluoric acid bath may be used to etch the electrode surfaces. By anetching process, electrodes 112 of finer widths may be obtained. Thisprocess also removes the oxide layer from the electrode surfaces andsmoothes those surfaces, a desirable step before forming additionalcoatings on array 110.

FIG. 3A shows electrodes 112 as having a tapered shape at their tips. Inan exemplary embodiment, each electrode 112 may have a width of about 80μm and taper to a point over the top 50 μm of its length. Further, FIG.3A also shows that a base section of electrodes 112 may have a platformportion 312. Portions 312 may serve as a platform for securing a supportlayer, which is described below with respect to FIGS. 3B and 3C. Ratherthan having platforms 312, however, electrodes 112 may include a steppedlower base portion (e.g., as shown in FIG. 3A-1) or a rounded lower baseportion (e.g., as shown in FIG. 3A-2), which may alternatively serve asa platform for supporting the support layer. Moreover, electrodes 112may have a variety of shapes, such as a continuous width shape (i.e.,with no platform or stepped base section), a conical shape, astepped-pyramidal shape, or a tapered shape different than that shown inFIG. 3A. Electrodes 112 may also have a variety of cross-sectionalshapes, such as a rounded cross-section (which may be formed by achemical etching process) or a rectangular, square, or hexagonalcross-section (which may be formed by the wire EDM technique). Moreover,as used herein, an electrode's “base section” refers broadly to the endportion of electrode 112 opposite the electrode's tip, without referringto the electrode's shape or width.

Electrodes 112 of array 110 may also differ in length to senseparticular neurons located at different depths in cortex 120. Forinstance, electrodes 112 may increase in length from one side of array110 to the other. Electrodes 112 may also vary in both length and widthfrom other electrodes in array 110, such that a given electrode 112 iseither longer or shorter, or wider or narrower, than the electrodeadjacent to it. For instance, array 110 may include shorter electrodesbetween 0.1 mm to 8 mm in length and/or longer electrodes between 0.3 mmto 50 mm in length. Further, for electrodes 112 to record signals fromcommon neurons, the spacing between electrodes may be less than 50 μm,while the spacing may be more than 400 μm when electrodes 112 recordsignals from different neurons.

Electrode arrays 110 consistent with the invention may also arrangeelectrodes 112 in a number of ways. For example, electrodes 112 may bearranged in a one-dimensional or two-dimensional matrix, according to apredefined pattern, or in a random order. One exemplary pattern in whichelectrodes 112 may be arranged is a honeycomb-like hexagonal pattern. Asdescribed above, however, any type of pattern or arrangement ofelectrodes 112 may be used to form array 110.

Depending upon the composition of conductive material 310, electrodes112 may be coated with a separate conductive layer (not shown). Theconductive layer may only be necessary if conductive material 310 is notbiocompatible with the neural tissue and cerebro-spinal fluid or if theelectrical characteristics require a coating (e.g., to avoid junctionpotentials at the electrode tips). An exemplary embodiment may includecoating electrodes 112 with platinum by an electroplating process orother deposition method. The deposited layer may also improve thesensitivity of the electrode and may also prevent oxidation of theelectrode. Electrode arrays 110 consistent with the present inventionmay also use other conductor materials besides platinum, such as gold ortitanium nitride, formed by electroplating or other types of formationprocesses, such as vapor deposition or electron beam deposition.Further, the entire structure of FIG. 3A or just the tips of electrodes112 may be coated with the conductive material.

An insulating layer (not shown) may also be applied to electrodes 112.Except for the electrode tip used to record the neural signals, theinsulating layer may cover the whole electrode. The insulating layer maybe removed from the electrode tips (e.g., by laser ablation, plasmaetching, or chemical etching), or may be prevented from being formed onthe tips (e.g., by a masking procedure). In this, way, conduction isallowed only through the tips and single neurons can be better isolatedfrom one another. In the exemplary embodiment, all but the top 50 μm ofeach electrode 112 are insulated with Paralene by a vapor depositionprocess. Other insulating materials, such as glass, silicon nitride,polyimide, an epoxy, or other plastics or ceramics, may be used instead.

As shown in FIG. 3B, a support layer 320 may then be placed overelectrodes 112 to electrically isolate electrodes 112 and to supportelectrodes 112 during the cutting process described below with respectto FIG. 3C. Layer 320 may have a number of corresponding openings forreceipt of electrodes 112. Support layer 320 may slide down overelectrodes 112 until, for example, it reaches the bottom platformsections 312 of each electrode 112. Each hole or opening in layer 320may have a diameter sized to securely receive each electrode 112, whilecompensating for any positional tolerances from a drilling or laserprocess when forming the holes. In the exemplary embodiment, supportlayer 320 is a flexible material, such as polyimide, parylene, orsilicone. Layer 320 may also be formed using materials having aflexibility that changes over time or under some other condition (e.g.,having a flexibility that changes in response to the brain's heat).

An optional step may include applying an epoxy coating (not shown) toelectrodes 112 and support layer 320. The epoxy coating may, however, beapplied after electrodes 112 are cut as described below with respect toFIG. 3C. After support layer 320 has been placed over electrodes 112,the bases of electrodes 112 may be cut using a wire EDM technique toseparate electrodes 112 from block 310. FIG. 3C illustrates array 110after electrodes 112 have been cut or separated from block 310.

After cutting electrodes 112, wiring 116 may then be placed over the cutends of electrodes 112, as shown in FIG. 3D, to connect electrodes toprocessing unit 114. Like support layer 320, wiring 116 may have anumber of corresponding openings for receipt of electrodes 112. WhileFIG. 3 shows these openings as passing entirely through wiring 116, theopenings may alternatively be formed as depressions in wiring 116, suchthat electrodes 112 may fit within the opening or depression, but notpass entirely through wiring 116. In either case, each hole or openingmay have a diameter sized to securely receive each electrode 112, whilecompensating for any positional tolerances from a drilling or laserprocess when forming the holes. Wiring 116 may then slide overelectrodes 112 until, for example, it reaches the platform sections 312of each electrode 112. Wiring 116 may then be electrically connected toelectrodes 112. Further, the cut array assembly may be placed in aholder (not shown) to hold electrodes 112 in place when aligning andlowering wiring 116 over electrodes 112. In the exemplary embodiment,wiring 116 may also be formed of a flexible material, such as polyimide,parylene, or silicone. Wiring 116 is described in more detail below withrespect to FIGS. 5A and 5B.

FIGS. 4A to 4G illustrate alternative, exemplary manufacturingprocessing steps, consistent with an embodiment of the presentinvention, for making an electrode array. In particular, FIG. 4A shows ablock of electrically conductive material 310 including a plurality ofelectrodes 112. The electrodes of FIG. 4A may be formed using theprocesses described above with respect to FIG. 3A. As shown in FIG. 4A,however, electrodes 112 have a stepped-pyramidal shape similar to thatshown in FIG. 3A-1, in which the electrodes 112 have stepped decreasesin width from bottom to top. In an exemplary embodiment, each electrode112 may have a tapered tip portion 412 and stepped base sections 414,416, and 418 of increasing widths. As described above, however,electrodes 112 may have a variety of shapes, including continuous widthshapes and stepped-pyramidal shapes having more or less than the threedifferent width sections shown in FIG. 4A. Moreover, as stated above, anelectrode's “base section” refers broadly to the end portion ofelectrode 112 opposite the electrode's tip, without referring to theelectrode's shape or width.

As shown in FIG. 4B, wiring 116 may then be placed over electrodes 112.As shown in FIG. 4B, and as described above with respect to FIG. 3D,wiring 116 may have a number of corresponding openings 420 for receiptof electrodes 112. Wiring 116 may slide down over electrodes 112 until,for example, it reaches the bottom base section 418 of each electrode112. FIG. 4C illustrates wiring 116 in its lowered position.

FIG. 4D shows an optional step of applying an epoxy coating 430 toelectrodes 112 and wiring 116. Epoxy coating 430 may, however, beapplied after electrodes 112 are cut as described below with respect toFIG. 4F. FIG. 4E shows the epoxy coating 430 lowered until it rests ontop of wiring 116. While FIGS. 4D and 4E show epoxy coating 430 ashaving a sheet-like form, epoxy 430 may take a variety of forms, such asa more fluid-like form for coating array 110. After wiring 116 and epoxycoating 430 have been placed over electrodes 112, electrodes 112 may becut along dashed line 440 shown in FIG. 4F by using a wire EDMtechnique. After cutting electrodes 112, their cut ends form squareconnector pads 442 which may then be soldered or otherwise electricallyconnected to the electrical contacts of wiring 116. FIG. 4G showselectrode array 110 after electrodes 112 have been cut.

By fabricating electrode array 110 according to the manufacturingmethods discussed above with respect to FIGS. 3A-3D and FIGS. 4A-4G,array 110 may have an improved degree of flexibility over conventionalfixed electrode arrays. This improved flexibility may be created bysupporting the electrodes 112 removed from base 310 with either-supportlayer 320 or flexible wiring 116. In particular, electrodes 112 areessentially supported and held together by their being inserted into theopenings of support layer 320 or flexible wiring 116. Because layer 320and wiring 116 can each be made flexible, array 110 can also then beflexible. This flexibility is an important feature of the presentinvention since it allows array 110 to better conform to the contours ofthe patient's brain and to be more compliant near blood vessels.However, systems and methods consistent with the invention may useelectrode arrays 110 with limited flexibility.

Moreover, electrode arrays 110 consistent with the present invention maybe manufactured by methods other than those discussed above with respectto FIGS. 3A-3D and FIGS. 4A-4G. For example, after fabricatingelectrodes 112, the base section of each individual electrode may beattached directly to a surface of wiring 116. According to thisalternative manufacturing method, wiring 116 would not need anythrough-hole (e.g., opening 420) for receiving electrodes 112. The endof each electrode 112 may simply be placed on the surface of wiring 116for attachment (e.g., by a bumping or soldering method).

FIGS. 5A and 5B illustrate an exemplary embodiment of a wiring 116consistent with the present invention. As shown in FIG. 5A, wiring 116may include openings 420 for receiving electrodes 112 of array 110. Aconductor 510 is connected to each opening 420 for transferring theneural signals received from an electrode 112 inserted into thecorresponding opening. Conductors 510 may then connect to processingunit 114 using, for example, fine-pitch surface mount connectors.

As described above, wiring 116 may be flexible circuit board ormicro-ribbon cable made of polyimide, parylene, or silicone. In oneexemplary embodiment, wiring 116 may comprise a single conductive layerof a polyimide-based flexible substrate having, for example, a thicknessof up to approximately a 200 μm, and include conductors 510 having abouta 25-50 μm diameter with a spacing of about 25-150 μm between adjacentconductors. This exemplary embodiment of wiring circuit 116 provides fora wiring connector having small dimensions and flexibility, while alsohaving a good yield during manufacturing. Wiring circuits 116 consistentwith the invention are not limited to these sizes, however, and thoseskilled in the art will appreciate that other sizes and types of wiringcircuits may be used to connect electrode array 110 to processing unit114.

A milling or laser machining process may then be used to createcorresponding openings 420 for each conductor 510. In the exemplaryembodiment, each opening 420 in wiring 116 may have a diameter sized tosecurely receive each electrode 112, while compensating for anypositional tolerances from a drilling or laser process when forming theholes.

As shown in FIG. 5B, wiring 116 may also include slits 520 betweenconductors 510 at various points along the length of wiring 116. Asshown in FIG. 5B, slits 520 may provide circuit 116 withthree-dimensional flexibility to help reduce tethering forces describedbelow. Slits 520 may be made by using a laser to make cuts on wiring 116between the parallel conductors 510. Slits 520 may run up to the lengthof wiring 116. To prevent excessive bending of wiring 116 near itsattachment to electrode array 110, a stiffener may also be added towiring 116. For instance, a hardening resin or epoxy may be applied tothe area where wiring 116 attaches to electrode array 110, as alsodiscussed above with respect to FIG. 4D.

The flexibility between electrode array 110 and processing unit 114created by wiring 116 offers several advantages. For instance, wiring116 may reduce tethering forces created when the brain moves relative tothe skull. If not reduced, these tethering forces may cause the positionof electrode array 110 to move relative to the brain. To reduce theseforces, an exemplary embodiment of wiring 116 has a horizontally flatshape where its width is much larger than its thickness. Wiring 116 thushas a lower stiffness for up-down brain shifts. Accordingly, by makingslits 520 of sufficient lengths, wiring 116 may have minimum stiffnesswithin the maximum expected range of motion. Wiring 116 may then allowelectrode array 110 to move with the brain as it shifts relative to theskull. In this way, brain implant systems of the present invention maysustain relative brain shifts of up to 2 mm, which may result fromcardiac and respiratory rhythms or other mechanical perturbations.Further, as an alternative to slits 520, wiring 116 may be coiled alongits length or bent into an accordion-style staircase.

In an exemplary embodiment, a flip chip mounting method based on studbumping or other bumping method may be used to connect wiring 116 toelectrodes 112 of array 110. FIGS. 6A and 6B illustrate exemplary studbumping mounting methods for the respective arrays manufacturedaccording to the processing steps of FIGS. 3A to 3D and the processingsteps of FIGS. 4A to 4G. Those skilled in the art will appreciate,however, that FIGS. 6A and 6B are intended to be exemplary of how knownbumping techniques may be used to connect wiring 116 to array 110.Further, other, attachment methods may also be used to mount wiring 112to the array 110, such as by using a conductive epoxy.

FIG. 6A shows an electrode 112 inserted through an opening of supportlayer 320, as described above with respect to FIGS. 3B and 3C. To mountwiring 116, electrical contact pads 610 may be formed on wiring 116 nearthe openings 420 for receiving electrodes 112. Solder bumps 612 may thenbe disposed on pads 610. When wiring 116 is then placed against platformportions 312 of electrodes 112, solder bumps 612 are deformed and createan electrical connection between pads 610 and platform portions 312 ofelectrodes 112. While FIG. 6A shows contact pads 610 and solder bumps612 placed on the side of wiring 116 facing support layer 320, pads 610and bumps 612 may alternatively be placed on the other side of wiring116 for connecting wiring 116 to electrodes 112.

In the exemplary embodiment of FIG. 6B, electrode 112 may be insertedthrough an opening 420 of wiring 116 until, for example, platformportion 312 of electrode 112 makes contact with electrical contact pads610 formed on wiring 116 and mates with wiring 116. Solder 612, or otherwire bonding methods or materials, may then be added to secure theelectrical connection of electrode 112 to pads 610 and hence to wiring116. A biocompatible polymer layer 620 may then be added on top ofwiring 116 and an epoxy 630 may be applied to the space betweenelectrode 112 and the opening 420 in wiring 116. Epoxy 630 may holdelectrodes 112 in place for the cutting process described above withrespect to FIGS. 4F and 4G. Further, this arrangement may cause anyoverflow of epoxy 630 from going between wiring 116 and thebiocompatible polymer layer 620. By doing so, this will prevent epoxy630 from leaking beyond the bottom of wiring circuit 116 and breakingthe electrical contact between electrode 112 and the pads 610.

Accordingly, wireless brain implant systems and methods for using andmanufacturing the same, have been described above. While this inventionhas been particularly shown and described with references to preferredembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the scope of the invention encompassed by the appendedclaims. For example, array 110 may be used to supply electrical impulsesignals to cortex 120 in addition to sensing neural signals. Thus, array110 may be used with neural stimulation techniques and tools known tothose skilled in the art.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1-28. (canceled)
 29. An electrode array, comprising: a nonconductivelayer; an array of electrodes, each electrode having a base section anda tip section, wherein the base section of each electrode is insertedinto the nonconductive layer, such that the electrodes are held togetherby the nonconductive layer; and an electrical connection located on thebase section of each electrode to communicate with the respectiveelectrode.
 30. The array of claim 29, wherein the nonconductive layercomprises a wiring layer.
 31. The array of claim 30, wherein the wiringcircuit further includes a nonconductive portion and a plurality ofconductors supported by the nonconductive portion and for connecting torespective ones of the plurality of electrodes, and wherein thenonconductive portion supports the plurality of electrodes.
 32. Thearray of claim 29, wherein the nonconductive layer is comprises anepoxy.
 33. The array of claim 29, wherein the nonconductive layer iscomprises glass.
 34. The array of claim 29, wherein the nonconductivelayer comprises a flexible material.
 35. The array of claim 34, whereinthe flexible material comprises at least one of polyimide, parylene, andsilicone.
 36. The array of claim 29, wherein the electrodes are arrangedin a two-dimensional matrix pattern.
 37. The array of claim 29, whereinthe electrodes are arranged in a honeycomb-like hexagonal pattern. 38.The array of claim 29, wherein the distances between neighboringelectrodes varies.
 39. The array of claim 29, wherein the electrodesincrease in length from one side of the array to another side of thearray.
 40. The array of claim 29, wherein the plurality of electrodeshave varying lengths.
 41. The array of claim 40, wherein a firstelectrode has a length different that than of its immediatelyneighboring electrodes.
 42. The array of claim 40, wherein the lengthsof the plurality of electrodes are random.
 43. The array of claim 29,wherein the plurality of electrodes have varying widths.
 44. The arrayof claim 43, wherein a first electrode has a width different than thatof each of its immediately neighboring electrodes.
 45. The array ofclaim 29, wherein the electrodes have a platform portion where the widthof the electrode is enlarged.
 46. The array of claim 45, wherein thenonconductive layer rests on the platform portion of each electrodeafter the base section of each electrode is inserted into thenonconductive section.
 47. The array of claim 29, wherein the electrodesmay apply an electrical stimulation signal.
 48. The array of claim 29,wherein the electrodes may detect an electrical signal. 49-58.(canceled)